PHOTOEMISSION-STUDY OF THE SIO2/SI INTERFACE STRUCTURE OF THIN OXIDE-FILMS ON SI(100), (111), AND (110) SURFACES

The SiO2/Si interface structure of thin oxide films thermally grown on Si(100), (111), and (110) surfaces under device processing conditions has been investigated using high-resolution photoemission spectroscopy with synchrotron radiation. The intensity distribution of the so-called suboxides, Si1+, Si2+, Si3+, displays a strong dependence on the crystallographic orientation of the substrate over the oxidation temperature range from 600 to 900-degrees-C; Si1+ is enhanced in intensity on Si(111) and (110), while the Si2+ intensity is larger than the Si1+ one on Si(100). This orientation dependence is explained in terms of the bond topology of the substrate surface. A Si(110) surface exhibits a rather large Si3+ intensity as compared to Si(100), (111) surfaces, suggesting that Si-Si bonds on the outermost layer of a Si(110) surface are easily broken by oxygen atoms to generate the bridge bond Si-O-Si. The presence of an interfacial Si atom to which hydrogen is bonded is clearly observed. The total suboxide intensity, i.e., the sum of the suboxide intensities depends on both oxidation temperature and substrate orientation, which is interpreted by means of the interfacial roughness and the surface Si atom density of the substrate. It is shown that an ordered crystalline phase of SiO2 is present at the interfacial region. The generation of this phase has a Si(111)-preferred orientation.